The International Monetary Fund warned policymakers to be on guard for the next recession even as it predicted global growth will accelerate to the fastest pace in seven years as U.S. tax cuts spur businesses to invest. The fund raised its forecast for world expansion to 3.9 percent this year and next, up 0.2 percentage point both years from its projection in October. That would be the fastest rate since 2011, when the world was bouncing back from the financial crisis. The strengthening recovery offers a “perfect opportunity now for…